In this specification the term “transponder” is used to describe a device that transmits and/or receives signals.
UHF (Ultra High Frequency) RFID systems are known in which a plurality of RFID transponders are activated by a UHF energizing or interrogation signal from an RFID interrogator. The transponders then transmit response signals to a receiver, which typically form part of an RFID interrogator. The response is achieved by so-called “backscattering”, i.e. the transponder reflects varying amounts of the incident UHF power up signal according to the data to be transmitted back to the UHF interrogator by load modulation of its antenna. Examples of such UHF RFID systems are specified in the international ISO/IEC 18000-6 standard. Specifically, RFID transponders and systems complying with the ISO/IEC 18000-6C standard (equivalent to the EPC C1G2 standard) are widely used in supply chain management applications for item identification. One reason for the popularity of UHF RFID is the relatively long reading range (around 10 m) and good anti-collision rate (>100 items per second).
Despite its wide use, UHF RFID suffers from certain drawbacks. Specifically, UHF frequencies are reflected and/or absorbed by various materials and substances, e.g. metals and liquids, resulting in weak or multi-path signal propagation. Reading range is reduced, or items are not successfully identified by nature of them residing in nulls in the
UHF energizing field. UHF RFID systems therefore often perform less than satisfactorily when applied to items with high metal or moisture content.
Low frequency (LF) RFID transponders and systems are also known in which the transponders are powered up and respond at low frequencies (e.g. 125 kHz or 134 kHz). Examples can be found in the international ISO/IEC 18000-2 and ISO 11785 standards. LF energizing has an advantage over UHF energizing in that low frequencies are not absorbed and/or reflected by moisture and metals to the same extent as UHF. LF RFID, however, suffers from low response data rates (typically only 2 to 4 kbit/s) and very poor anti-collision rates. Reading range is also low (less than 1 m). LF RFID is therefore usually not suitable for supply chain applications.
High frequency (HF) RFID transponders and systems are also known in which the transponders are powered up and respond at high frequencies (typically 13.56 MHz). Examples can be found in the international ISO/IEC 18000-3, ISO/IEC 14443 and ISO/IEC 15693 standards. HF RFID supports better data and anti-collision rates than LF, but it is still low compared to UHF RFID. HF is also absorbed much more than LF in high moisture environments resulting in low reading range in such environments (typically less than 1 m). With a few exceptions HF RFID is therefore usually not suitable for supply chain applications, especially not in high metal and moisture content environments.
IP-X Dual Frequency or DF RFID is a unique proprietary technology that overcomes the drawbacks of the aforementioned UHF, LF and HF technologies. The transponders are powered at LF (i.e. around 125 kHz), resulting in good power-up range even in high moisture or metal content environments. Response is at HF (typically at 6.78 MHz) at high data rates (typically 128 kbit/s), resulting in anti-collision performance rivaling that of UHF systems. Examples can be found in European patent EP1393245, EP1927072 and EP1862945. In systems where the items to be indentified do contain large amounts of moisture or metal and where read reliability is important, DF RFID systems can compete with UHF RFID.
A subset of supply chain management involves the use of Returnable Transport Items (RTI), such as pallets or plastic crates and totes that need to be tagged with transponders for identification of the RTI during the various stages of the supply chain. RTIs typically move from a service provider that owns and maintains the RTIs to a producer where goods are packed or loaded, then to a distribution centre and finally to retailer, from where it returns empty to the service provider. During its life time an RTI can complete several such round trips, so the actual cost of the transponder becomes less important, since it is effectively reused several times. The main problem is that along this round trip, an RTI can encounter different RFID installations depending on its contents, need for accurate identification and installed infrastructure. Typically at certain points along the chain IP-X DF RFID systems can be in use, while at other points along the chain ISO/IEC 18000-6 UHF systems can be in use.
A transponder that can operate using either an ISO/IEC 18000-6 international standard UHF RFID protocol, or using an IP-X DF protocol, while supplying the same data in both cases, will solve the RTI problem. However, to achieve this is not easy, since UHF RFID and IP-X DF RFID operate at different supply voltages, and have very different memory architectures. Specifically, UHF RFID circuits can operate from supply voltages as low as 1 V, while IP-X DF requires at least 2 V. ISO/IEC 18000-6C uses a segmented memory architecture with 16 bit pages, while IP-X DF uses a flat memory architecture with 64 bit pages. ISO/IEC 18000-6C memory blocks can be read and write protected only at a block level, while IP-X memory can only be write protected, but at a page level.
There are many dual and multi-frequency as well as multi-protocol transponders described in prior art, e.g. U.S. Pat. No. 7,248,165, US2004/0089707, US2009/0066516, US2008/0218344, EP1821242, U.S. Pat. No. 6,223,990, EP0592224, US2009/045923, WO2005073906, EP0783158, US2007/176755, US2006/109085, US2004/185806 and EP1862945. However, none of these give any details as to how such a combination of an ISO/IEC 18000-6 and IP-X DF transponder could be realized or how to overcome the mentioned difficulties of such a combination.
Accordingly, it is an object of the present invention to provide a transponder, an RFID system and a method of operating a transponder allowing identification of RTIs in both IOS/IEC 18000-6 UHF and IP-X DF systems and which alleviates the problem of UHF energy absorption and reflection in ISO 18000-6 UHF RFID systems or which at least provides the public with a useful choice.